Many online transactions involve peer-to-peer transactions between private individuals. For example, digital noticeboards are popular for buying and selling used items. However, buyers and sellers may have limited contact before performing a P2P transaction. In these cases, it may be difficult for buyers and sellers to verify each party's identity to ensure that the transaction is not fraudulent. For example, the seller must trust that the buyer has access to the necessary funds to purchase the sales good, and that the buyer will hand over the agreed amount of money. With the proliferation of identity theft, some buyers may provide stolen payment details of another user, and the seller may be forced to return funds received after sold goods have already been handed over to a buyer. Further, the transactions may often occur using different payment applications with many user accounts. A buyer, for example, may provide an erroneous payment to an account that is not in fact associated with the intended seller, and then the buyer may have difficulty retrieving the erroneous payment. It would be desirable to provide a method of authenticating P2P transactions while ensuring the correct identity of each party to the transaction.